1. Field of the Invention
This invention relates to a control technology of a magnetic disk storage apparatus and further to a control technology of a voice coil motor for moving a magnetic head for conducting read/write of information from and to a storage track on a magnetic storage disk that is driven and rotated.
2. Description of the Related Art
A magnetic disk storage apparatus includes a magnetic head for executing read/write of information to and from a storage track on a magnetic storage disk driven and rotated, a voice coil motor for moving the magnetic head on the disk and a voice coil motor drive control apparatus for conducting positioning control of the magnetic head by controlling a driving current of a voice coil motor while a read state of the magnetic head is being monitored.
An information recording density of the magnetic disk storage apparatus has become higher and higher every year and higher accuracy has been required for positioning control of the magnetic head with the increase of the storage density. Therefore, feedback control that executes feedback control of a driving current of the voice coil motor on the basis of a detection value of the driving current and conducts positioning of the magnetic head has been employed. To drive the voice coil motor for moving the magnetic head, a linear driving system for continuously changing a driving current amount of the voice coil motor was employed at the beginning.
The time necessary for moving the magnetic head to a desired storage track, that is, a so-called “seek time”, must be shortened to accomplish a higher speed operation of the magnetic disk storage apparatus but the driving current of the voice coil motor must be increased to accomplish this object. When the driving current of the voice coil motor is increased, however, a power loss increases particularly in the motor coil and a calorific value increases with the power loss. The increase of a power source current resulting from the reduction of the seek time is remarkable in the linear driving system. On the other hand, pulse width modulation control (hereinafter called “PWM control”) is known as a method of reducing the power source required for moving the magnetic head. This PWM control needs lower power consumption than the linear driving system but is not free from the problem that precision control is difficult to practice.
To cope with the problem, a technology has been developed that drives the voice coil motor by PWM control during the so-called “seek operation” in which the magnetic head is moved to a predetermined storage track and drives the voice coil motor by the linear driving system during a track follow operation in which the magnetic head is allowed to follow the desired track for read/write (refer to patent document 1).
Patent document 1: JP-A-2002-184137